For several years, cosmetic products have been developed having rheological action on the skin, such as firmness, tonicity, elasticity or suppleness. The measurement of the efficacy thereof has for many years been assessed from different scientific angles such as clinical and instrumental approaches.
As far as women are concerned, numerous visual and sensory criteria are involved in the subjective phenomenon of skin firmness and elasticity.
For some, evaluation of skin texture is primarily indicative of firmness whilst others palpate their skin beneath their fingertips to assess its resistance or density. Some women will actually evaluate tissue firmness by looking at themselves in a mirror. Although all of these factors interact with each other, touch and sensation are still the two parameters most widely used to evaluate perceived firmness and elasticity. Furthermore, the dermatologist's specific and standardised approach towards clinical evaluation and skin sagging is based primarily on pinching the skin between two fingers.
From the instrument standpoint, some validated methods propose various ways of deforming the skin such as suction, twisting or stream of pressurized air. However, a frequent disadvantage associated with these methods is that the deformity is often limited to a small surface area of skin, which differs from the area assessed by women and/or the experts in their evaluation.
Thus the “firmness” perception includes many aspects that prior art approaches cannot significantly characterize in a whole. Another problem to be faced is that principal measuring techniques focus on the analysis of small skin surface areas and therefore lack a reliant correlation with the clinical evaluations.
To be closer in line with clinical evaluation of skin firmness as conducted both i) by individual on their sensed and perceived viscoelastic properties of the skin and ii) by dermatologists, the inventors have developed a novel quantitative approach combining both infrared thermography imaging and a skin pinching system.
The present invention intends to obtain more descriptive and quantitative data on perceived elasticity and other rheological properties such as firmness and tonicity.
In order to get information closer to consumers' perception, the present inventors have developed a new method using skin deformation system and infrared thermography imaging.